Typical automatic transmissions include a torque converter and a powertrain of a multiple speed gear mechanism connected to the torque converter. In addition, a hydraulic control system is provided at the automatic transmission for selectively operating at least one operational element included in the powertrain when the vehicle is running.
A variety of such powertrains and hydraulic control systems have been developed by vehicle manufactures according to their own schemes. Currently, four-speed automatic transmissions are most often found in the market. However, a five-speed automatic transmission is also available for the power transmission performance enhancement and for enhanced fuel mileage of a vehicle.
Building on such five-speed automatic transmissions, six-speed automatic transmissions are currently under investigation to further enhance the performance of a power transmission of an automatic transmission, and, thereby increase fuel mileage of the vehicle.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known in this country to a person of ordinary skill in the art.